The present invention relates to a method and apparatus for producing an air textured yarn having a relatively low residual shrinkage.
Methods and apparatus are known from German Patent 32 10 784, in which the yarn to be textured is supplied as a preoriented, thermoplastic yarn. The yarn is drawn in a draw zone and subsequently extended in an air nozzle to form loops, curls, bows and the like. The yarn produced has a residual shrinkage. In the scope of the present application, the phase "residual shrinkage" is intended to mean the tendency (shrinkage tendency) of the yarn to shrink when being heated, for example, by hot air or hot water.
Shrinkage is a shortening of the yarn, which occurs in fact when it is heated, and which is expressed by the formula (L1-L2).times.100/L1%, with L1being the original and L2 the shortened length of the yarn. The shrinkage cannot be greater than the previously existing residual shrinkage. However, a residual shrinkage can still remain despite the shrinkage.
If the known method is applied, the residual shrinkage, i.e. the tendency to shrink can be reduced only by a suitable aftertreatment subsequent to the process. Although it is possible to reduce the residual shrinkage of the yarn by such measures for aftertreatment of the shrinkage, these measures, however, have considerable disadvantages. This applies particularly to textured yarns, since the aftertreatment subsequently affects or even damages the crimp. Primarily, a shrinkage treatment can be carried out intensively only when the yarn is subjected to "contact heating," i.e. when the yarn passes over a hot plate of a heated godet. However, this procedure is generally not suitable for textured yarns, because it results in an ironing effect. This means that a previously imparted yarn texture is again removed in part, primarily on one side of the yarn, by its contact with the hot surface.
A method of aftertreatment for the purpose of reducing the shrinkage of an air textured yarn is known from U.S. Pat. No. 3,892,020 which corresponds to DE-OS 23 59 102. In this process, the air textured yarn is wound onto a very soft package under little tension of less than 0.4 grams/denier. This package is subsequently dyed in a heated dye liquor. As a result thereof a shrinkage is started, and the residual shrinkage remaining in the yarn is reduced accordingly. However, this method is not adapted to carry out the treatment for reducing the residual shrinkage on an air texturing machine. Particularly disadvantageous is that the package must be wound under a low yarn tension, which adversely affects the transportability of the package. Furthermore, the package and the yarn are damaged by the increased yarn tension, which builds as the shrinkage becomes effective.
The residual shrinkage can also be reduced prior to texturing. To this end, it is known that a thermoplastic drawing process of thermoplastic yarns can be followed by a treatment for reducing shrinkage in a relaxation zone. The relaxation zone follows the actual draw zone, and is formed between two godets or feed systems, with the yarn being heated in the relaxation zone. As a result thereof the length of the yarn path and thus the height of the air texturing machine is necessarily increased. Primarily, however, this relaxation treatment will always result in the problem that the reduction of the shrinkage in such a relaxation zone has its limits, inasmuch as the tension of a yarn traveling between godets cannot be reduced to any desired extent, and consequently the shrinkage is dependent on the limited speed difference of the godets.
The above is based on the fact that a yarn must always advance in a straight line between two feed systems and consequently be under a certain minimum tension. The shrinkage which occurs in fact results from the state of equilibrium between the shrinkage tendency on the one hand and the yarn tension on the other.
A method of reducing residual shrinkage, in which a multifilament yarn is simultaneously interlaced or entangled, is disclosed in U.S. Pat. No. 3,069,836. In this method, the yarn, which is first drawn between two godets assisted by an unheated draw pin, passes through a relaxation zone, in which the entry speed is greater than the exit speed. While in the relaxation zone, the yarn passes through a nozzle, which is supplied by a heated gas. The shrinkage which is this accomplished is, as aforesaid, dependent on the difference of these speeds. The application of hot air serves both to produce a shrinkage and to make a yarn which has its filaments entangled. The method is not suitable for producing a crimp, because it will produce a yarn whose filaments are chemophysically changed in their inner structure by the action of heat during the air texturing operation. Even if curls and loops were produced in the filaments, such a crimp of this yarn would not be stable. This means that this crimp would again be removed from the yarn by the application of tensile forces. Tensile forces, which suffice to remove this crimp, however, occur already as a result of the shrinkage in the relaxation zone, as well as also during the aftertreatment by subsequent stabilizing and heat setting processes, which are provided, according to U.S. Pat. No. 32,047, for improving the length stability of the yarn, and in particular in weaving and knitting. As a result, such a yarn would not be usable as a crimped yarn.
An air texturing method in the meaning of the present application is understood to be a method, in which a continuous, synthetic yarn, which comprises a plurality of individual filaments, is subjected to the action of an air texturing nozzle. In the air texturing nozzle, an unheated air jet is blown onto the yarn. As a result, the individual filaments are deformed to loops, curls, bows or the like without thereby substantially changing the chemophysical structure of the filaments. The filaments extending substantially parallel at first are only geometrically relocated in an irregular form, thereby forming in particular loops, curls and bows. A particularly suitable method of producing high-quality yarns is disclosed in German Patent 27 49 867 and corresponding U.S. Pat. No. 32,047. Suitable nozzles are shown in the dissertation "Die Texturierung von Filamentgarnen im Luftstrom" by Bock, Aachen 1984/1985.
It is accordingly an object of the present invention to efficiently produce an air textured yarn, which is low in shrinkage, i.e., has little residual shrinkage.